One of the London stock market's most prominent oil exploration companies has been rocked by a boardroom probe into unauthorised payments.

Sky News understands that Afren, which has operations in Nigeria and other parts of Africa, will disclose on Thursday that Osman Shahenshah, its chief executive, and Shahid Ullah, chief operating officer, have been suspended.

A statement is expected ahead of the start of trading in shares in the FTSE-250 company, which has a market value of £1.7bn.

The crisis could ignite another debate about corporate governance standards among overseas resources companies listed in London following a string of damaging disputes.

Sources said that an independent review carried out by Wilkie Farr & Gallagher, a law firm, had identified the receipt of payments which Afren's board suspected were for the benefit of the two executives.

They added that the announcement of Afren's half-year results on August 4 would be postponed as a result of the news.

The company is understood to be planning to appoint Egbert Imomoh as executive chairman and Toby Hayward, currently senior independent director, as interim chief executive while the investigation proceeds.

Shares in Afren have been buoyed by persistent takeover speculation, although they have risen relatively modestly during the last year.